List of query params with Flask request.args

Question

I am trying to pass comma separated query parameters to a Flask endpoint.

An example URI would be:

localhost:3031/someresource#?status=1001,1002,1003

Looking at the return of request.args or request.args.getlist('status') I see that I only get a string.

ipdb> pp request.args
ImmutableMultiDict([('status', '1001,1002,1003')])
ipdb> request.args.getlist('status')
['1001,1002,1003']

I know I can split the string by comma but that feels hacky. Is there a more idiomatic way to handle this in Flask? Or are my query params wrong format?

Solution
Since Flask does not directly support comma separated query params, I put this in in my base controller to support comma-separated or duplicate query params on all endpoints.

request_data = {}
params = request.args.getlist('status') or request.form.getlist('status')
if len(params) == 1 and ',' in params[0]:
    request_data['status'] = comma_separated_params_to_list(params[0])})
else:
    request_data['status'] = params

def comma_separated_params_to_list(param):
    result = []
    for val in param.split(','):
        if val:
            result.append(val)
    return result

Answer 1

Its not uncommon REST API design to have commas to pass multiple values for the same key - makes it easier for the user. You're parsing GET args anyway, parsing strings is not that much more hacky. You can choose to raise a 400 HTTP error if their string with commas isn't well formatted.

Some other languages (notably PHP) support 'array' syntax, so that is used sometimes:

/request?status[]=1000&status[]=1001&status[]=1002

The flask variant getlist expects multiple keys:

from flask import Flask, request

app = Flask(__name__)

@app.route('/')
def status():
    first_status = request.args.get("status")
    statuses = request.args.getlist("status")
    return "First Status: '{}'\nAll Statuses: '{}'".format(first_status, statuses)

❯ curl "http://localhost:5000?status=5&status=7"
First Status: '5'
All Statuses: '['5', '7']'

There's no standard for this, how multiple GET args are parsed/passed depends on which language/framework you're using; flask is built on werkzeug so it allows this style, but you'll have to look it up if you switch away from flask.

Answer 2

This is what you might want here:

request.arg.to_dict(flat=False)

flat is True by default, so by setting it to False, you allow it to return a dict with values inside a list when there's more than one.

According to to_dict documentation:

 to_dict(flat=True)

    Return the contents as regular dict. If flat is True
    the returned dict will only have the first item present, if flat is False
    all values will be returned as lists.